The above are two solenoids consisting of a coil of insulated wire wrapped around a ferromagnetic core. The current flowing into the two coils has the same current intensity of \(I\). The central axis of the two cores are the same and the point P is the center of the two cores. Which of the following explanations is correct?
a) The magnetic moments of the atoms of the two ferromagnetic cores line up to the right.
b) Attractive forces arise between the two ferromagnetic cores.
c) If we turn off the switch, the magnetic field at point P disappears.